1. Field of the Invention
The invention relates to a bar arrangement for a machine for the production of a fibrous web, especially a paper, cardboard or tissue web, which extends transversely to the machine direction and which comprises at least one fixed structure which is mounted directly or indirectly to a frame of the machine; at least one movable bar which is connected preferably indirectly with the fixed structure, relative to which it is preferably movable by means of a controllable/adjustable actuation device, at least between an inoperative position and an operating position in which the movable bar can be pressed against an element by means of a selectable contact force; and at least one fixed guide device which is mounted rigidly on the fixed structure or directly or indirectly on the frame of the machine and which has a guiding effect upon the movable bar and which includes several fixed c-shaped guide units located at a distance from each other, which surround the movable bar on one side in its lower area, at least in sections, with at least one fixed guide arm.
2. Description of the Related Art
The invention further relates to a wire section for a machine for the production of a fibrous web and a machine for the production of a fibrous web. The fibrous web can in particular be a paper, cardboard or tissue web.
A bar arrangement of this type is known for example from the German disclosure document DE 40 19 884 A1. The movable bar described in this document is a forming bar and the element is a forming wire located in the area of a twin wire zone in a twin wire section. This bar arrangement comprises a fixed guide arrangement which guides the movable bar, especially the forming bar and which includes several fixed c-shaped guide units located at a distance from each other, which surround the movable bar, especially the forming bar on one side in its lower area, at least in sections, with at least one fixed guide arm.
The movable bar, in particular the forming bar disclosed in the aforementioned documentation serves among other uses to scrape away and remove water from an element, particularly a forming wire shortly after the start of the sheet formation process in a machine for the production of a fibrous web, especially a paper, cardboard or tissue web. In addition it exerts an impulse upon the fiber/water suspension in order to thereby exercise targeted influence on the sheet characteristics. In its operating position the movable bar, in particular the forming bar is for this purpose positioned and preferably pressed against the element at a controlled, or respectively adjusted selectable contact force. The positioning and lastly the pressing contact of the movable bar, particularly the forming bar, preferably the lifting movement of the movable bar, particularly the forming bar is generally conducted by an actuation device, especially by one or two tubes which are filled with a gaseous or liquid medium and which move the movable bar, particularly the forming bar forward into the operating position.
For maintenance purposes, for example replacement of the element, especially wire replacement or its own replacement, the movable bar, particularly the forming bar must be capable of being pulled back from the element, particularly from the forming wire and capable of being brought into an inoperative- or servicing position. Generally this occurs through deactivation of the actuation device and the effect of gravitation upon the movable bar, particularly the forming bar. Due, for example to the effects of frictional forces and/or contamination in the guide areas of the bar arrangement, and a possible unfavorable installation position of the bar arrangement it cannot always be assured that the movable bar, particularly the forming bar can be pulled back from the element, particularly the forming wire into the inoperative- or servicing position in a process-reliable and reproducible manner.
In addition, the friction between the guide surfaces of the lateral guides and the movable bar, particularly the forming bar causes said bar—not only at a slightly slanted installation position to not always be pulled back reliably from the element, particularly the forming wire through gravitation when discharging the medium from the actuation device.
What is needed in the art is to further develop a bar arrangement of the type referred to at the beginning so that the known disadvantages of the state of the art are largely, preferably completely removed. In particular, a process-reliable, reproducible and preferably cost effective retraction of the movable bar should be possible, particularly also during operation of the machine for the production of a fibrous web.